The purpose of this proposal is to develop a modification of Teller's forced-choice preferential (FPL) looking procedure, to allow clinical assessment of visual acuity in human infants. Four types of studies are in progress: 1. Clinically related studies conducted in the laboratory - Tests of premature infants suggest that acuity should be evaluated based on the infant's age from the date it was due to be born and not on the infant's actual age from birth. Preliminary norms for monocular testing will be established on presumptively normal infants born at term. A procedure for testing children between 6 months and two years of age is being developed. 2. Testing of infants in clinical settings - The clinical usefulness of the procedure and the applicability of preliminary laboratory norms to patient populations is being assessed through tests of infants seen as local well-baby and high-risk infant clinics. 3. Basic laboratory studies - A study of the effects of stimulus luminance on acuity in infants is being carried out to define the extent to which luminance should be controlled during clinical testing. 4. Apparatus development - installation of a television camera and monitor system is planned. This will reduce test personnel from three to two.